Synthesis
GENERAL STEPS: Methyl 3-chlorothiophene-2-carboxylate (50 g, 0.28 mol) was dissolved in methanol (100 mL), aqueous sodium hydroxide solution (2M, 400 mL) was added slowly, and the reaction temperature was maintained at 0 °C. The reaction mixture was stirred at room temperature for 2 hours. After removal of methanol by distillation under reduced pressure, the aqueous phase was washed with ether and subsequently acidified with 2N hydrochloric acid to pH < 3. The precipitated white solid was collected by filtration and dried under vacuum to give 3-chlorothiophene-2-carboxylic acid (45 g, 98% yield). Mass spectrometry (MS) analysis showed a molecular ion peak (M+H+) of 163.
References
[1] Heterocycles, 1985, vol. 23, # 6, p. 1431 - 1435
[2] Patent: WO2012/139425, 2012, A1. Location in patent: Page/Page column 119
[3] Heterocycles, 2007, vol. 71, # 1, p. 87 - 104
[4] Patent: WO2013/28670, 2013, A1. Location in patent: Page/Page column 96
[5] Patent: US9181236, 2015, B2. Location in patent: Page/Page column 107
